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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) ** Obsolete normative reference: RFC 8499 (Obsoleted by RFC 9499) -- Obsolete informational reference (is this intentional?): RFC 2845 (Obsoleted by RFC 8945) Summary: 1 error (**), 0 flaws (~~), 1 warning (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group W. Kumari 3 Internet-Draft Google 4 Intended status: Standards Track E. Hunt 5 Expires: November 6, 2020 ISC 6 R. Arends 7 ICANN 8 W. Hardaker 9 USC/ISI 10 D. Lawrence 11 Oracle + Dyn 12 May 05, 2020 14 Extended DNS Errors 15 draft-ietf-dnsop-extended-error-16 17 Abstract 19 This document defines an extensible method to return additional 20 information about the cause of DNS errors. Though created primarily 21 to extend SERVFAIL to provide additional information about the cause 22 of DNS and DNSSEC failures, the Extended DNS Errors option defined in 23 this document allows all response types to contain extended error 24 information. Extended DNS Error information does not change the 25 processing of RCODEs. 27 Status of This Memo 29 This Internet-Draft is submitted in full conformance with the 30 provisions of BCP 78 and BCP 79. 32 Internet-Drafts are working documents of the Internet Engineering 33 Task Force (IETF). Note that other groups may also distribute 34 working documents as Internet-Drafts. The list of current Internet- 35 Drafts is at https://datatracker.ietf.org/drafts/current/. 37 Internet-Drafts are draft documents valid for a maximum of six months 38 and may be updated, replaced, or obsoleted by other documents at any 39 time. It is inappropriate to use Internet-Drafts as reference 40 material or to cite them other than as "work in progress." 42 This Internet-Draft will expire on November 6, 2020. 44 Copyright Notice 46 Copyright (c) 2020 IETF Trust and the persons identified as the 47 document authors. All rights reserved. 49 This document is subject to BCP 78 and the IETF Trust's Legal 50 Provisions Relating to IETF Documents 51 (https://trustee.ietf.org/license-info) in effect on the date of 52 publication of this document. Please review these documents 53 carefully, as they describe your rights and restrictions with respect 54 to this document. Code Components extracted from this document must 55 include Simplified BSD License text as described in Section 4.e of 56 the Trust Legal Provisions and are provided without warranty as 57 described in the Simplified BSD License. 59 Table of Contents 61 1. Introduction and background . . . . . . . . . . . . . . . . . 3 62 1.1. Requirements notation . . . . . . . . . . . . . . . . . . 3 63 2. Extended DNS Error EDNS0 option format . . . . . . . . . . . 4 64 3. Extended DNS Error Processing . . . . . . . . . . . . . . . . 5 65 4. Defined Extended DNS Errors . . . . . . . . . . . . . . . . . 5 66 4.1. Extended DNS Error Code 0 - Other . . . . . . . . . . . . 6 67 4.2. Extended DNS Error Code 1 - 68 Unsupported DNSKEY Algorithm . . . . . . . . . . . . . . 6 69 4.3. Extended DNS Error Code 2 - Unsupported DS 70 Digest Type . . . . . . . . . . . . . . . . . . . . . . . 6 71 4.4. Extended DNS Error Code 3 - Stale Answer . . . . . . . . 6 72 4.5. Extended DNS Error Code 4 - Forged Answer . . . . . . . . 6 73 4.6. Extended DNS Error Code 5 - DNSSEC Indeterminate . . . . 6 74 4.7. Extended DNS Error Code 6 - DNSSEC Bogus . . . . . . . . 6 75 4.8. Extended DNS Error Code 7 - Signature Expired . . . . . . 6 76 4.9. Extended DNS Error Code 8 - Signature Not Yet Valid . . . 7 77 4.10. Extended DNS Error Code 9 - DNSKEY Missing . . . . . . . 7 78 4.11. Extended DNS Error Code 10 - RRSIGs Missing . . . . . . . 7 79 4.12. Extended DNS Error Code 11 - No Zone Key Bit Set . . . . 7 80 4.13. Extended DNS Error Code 12 - NSEC Missing . . . . . . . . 7 81 4.14. Extended DNS Error Code 13 - Cached Error . . . . . . . . 7 82 4.15. Extended DNS Error Code 14 - Not Ready . . . . . . . . . 7 83 4.16. Extended DNS Error Code 15 - Blocked . . . . . . . . . . 7 84 4.17. Extended DNS Error Code 16 - Censored . . . . . . . . . . 7 85 4.18. Extended DNS Error Code 17 - Filtered . . . . . . . . . . 8 86 4.19. Extended DNS Error Code 18 - Prohibited . . . . . . . . . 8 87 4.20. Extended DNS Error Code 19 - Stale NXDOMAIN Answer . . . 8 88 4.21. Extended DNS Error Code 20 - Not Authoritative . . . . . 8 89 4.22. Extended DNS Error Code 21 - Not Supported . . . . . . . 8 90 4.23. Extended DNS Error Code 22 - No Reachable Authority . . . 8 91 4.24. Extended DNS Error Code 23 - Network Error . . . . . . . 8 92 4.25. Extended DNS Error Code 24 - Invalid Data . . . . . . . . 9 93 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 94 5.1. A New Extended DNS Error Code EDNS Option . . . . . . . . 9 95 5.2. New Registry for Extended DNS Error Codes . . . . . . . . 9 96 6. Security Considerations . . . . . . . . . . . . . . . . . . . 12 97 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12 98 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 13 99 8.1. Normative References . . . . . . . . . . . . . . . . . . 13 100 8.2. Informative References . . . . . . . . . . . . . . . . . 13 101 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14 103 1. Introduction and background 105 There are many reasons that a DNS query may fail, some of them 106 transient, some permanent; some can be resolved by querying another 107 server, some are likely best handled by stopping resolution. 108 Unfortunately, the error signals that a DNS server can return are 109 very limited, and are not very expressive. This means that 110 applications and resolvers often have to "guess" at what the issue is 111 - e.g. was the answer marked REFUSED because of a lame delegation, or 112 because the nameserver is still starting up and loading zones? Is a 113 SERVFAIL a DNSSEC validation issue, or is the nameserver experiencing 114 some other failure? What error messages should be presented to the 115 user or logged under these conditions? 117 A good example of issues that would benefit from additional error 118 information are errors caused by DNSSEC validation issues. When a 119 stub resolver queries a name which is DNSSEC bogus [RFC8499] (using a 120 validating resolver), the stub resolver receives only a SERVFAIL in 121 response. Unfortunately, the SERVFAIL Response Code (RCODE) is used 122 to signal many sorts of DNS errors, and so the stub resolver's only 123 option is to ask the next configured DNS resolver. The result of 124 trying the next resolver is one of two outcomes: either the next 125 resolver also validates, and a SERVFAIL is returned again, or the 126 next resolver is not a validating resolver, and the user is returned 127 a potentially harmful result. With an Extended DNS Error (EDE) 128 option enclosed in the response message, the resolver is able to 129 return a more descriptive reason as to why any failures happened, or 130 add additional context to a message containing a NOERROR RCODE. 132 This document specifies a mechanism to extend DNS errors to provide 133 additional information about the cause of an error. These extended 134 DNS error codes are described in this document can be used by any 135 system that sends DNS queries and receives a response containing an 136 EDE option. Different codes are useful in different circumstances, 137 and thus different systems (stub resolvers, recursive resolvers, and 138 authoritative resolvers) might receive and use them. 140 1.1. Requirements notation 142 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 143 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 144 "OPTIONAL" in this document are to be interpreted as described in BCP 145 14 [RFC2119] [RFC8174] when, and only when, they appear in all 146 capitals, as shown here. 148 2. Extended DNS Error EDNS0 option format 150 This draft uses an EDNS0 ([RFC6891]) option to include Extended DNS 151 Error (EDE) information in DNS messages. The option is structured as 152 follows: 154 1 1 1 1 1 1 155 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 156 +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ 157 0: | OPTION-CODE | 158 +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ 159 2: | OPTION-LENGTH | 160 +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ 161 4: | INFO-CODE | 162 +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ 163 6: / EXTRA-TEXT ... / 164 +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ 166 Field definition details: 168 o OPTION-CODE, 2-octets/16-bits (defined in [RFC6891]]), for EDE is 169 TBD. [RFC Editor: change TBD to the proper code once assigned by 170 IANA.] 171 o OPTION-LENGTH, 2-octets/16-bits ((defined in [RFC6891]]) contains 172 the length of the payload (everything after OPTION-LENGTH) in 173 octets and should be 2 plus the length of the EXTRA-TEXT field 174 (which may be a zero-length string). 175 o INFO-CODE, 16-bits, which is the principal contribution of this 176 document. This 16-bit value, encoded in network (MSB) byte order, 177 provides the additional context for the RESPONSE-CODE of the DNS 178 message. The INFO-CODE serves as an index into the "Extended DNS 179 Errors" registry defined and created in Section 5.2. 180 o EXTRA-TEXT, a variable length, UTF-8 encoded [RFC5198], text field 181 that may hold additional textual information. This information is 182 intended for human consumption (not automated parsing). EDE text 183 may be null terminated but MUST NOT be assumed to be; the length 184 MUST be derived from the OPTION-LENGTH field. The EXTRA-TEXT 185 field may be zero octets in length, indicating that there is no 186 EXTRA-TEXT included. Care should be taken not to include private 187 information in the EXTRA-TEXT field that an observer would not 188 otherwise have access to, such as account numbers. 190 The Extended DNS Error (EDE) option can be included in any response 191 (SERVFAIL, NXDOMAIN, REFUSED, and even NOERROR, etc) to a query that 192 includes OPT Pseudo-RR [RFC6891]. This document includes a set of 193 initial codepoints, but is extensible via the IANA registry defined 194 and created in Section 5.2. 196 3. Extended DNS Error Processing 198 When the response grows beyond the requestor's UDP payload size 199 [RFC6891], servers SHOULD truncate messages by dropping EDE options 200 before dropping other data from packets. Implementations SHOULD set 201 the truncation bit when dropping EDE options. Because long EXTRA- 202 TEXT fields may trigger truncation (which is undesirable given the 203 supplemental nature of EDE) implementers and operators creating EDE 204 options SHOULD avoid lengthy EXTRA-TEXT contents. 206 When a resolver or forwarder receives an EDE option, whether or not 207 (and how) to pass along EDE information on to their original client 208 is implementation dependent. Implementations MAY choose to not 209 forward information, or they MAY choose to create a new EDE option(s) 210 that conveys the information encoded in the received EDE. When doing 211 so, the source of the error SHOULD be attributed in the EXTRA-TEXT 212 field, since an EDNS0 option received by the original client will 213 appear to have come from the resolver or forwarder sending it. 215 This document does not allow or prohibit any particular extended 216 error codes and information to be matched with any particular RCODEs. 217 Some combinations of extended error codes and RCODEs may seem 218 nonsensical (such as resolver-specific extended error codes in 219 responses from authoritative servers), so systems interpreting the 220 extended error codes MUST NOT assume that a combination will make 221 sense. Receivers MUST be able to accept EDE codes and EXTRA-TEXT in 222 all messages, including those with a NOERROR RCODE, but need not act 223 on them. Applications MUST continue to follow requirements from 224 applicable specifications on how to process RCODEs no matter what EDE 225 values are also received. Senders MAY include more than one EDE 226 option and receivers MUST be able to accept (but not necessarily 227 process or act on) multiple EDE options in a DNS message. 229 4. Defined Extended DNS Errors 231 This document defines some initial EDE codes. The mechanism is 232 intended to be extensible, and additional code-points can be 233 registered in the "Extended DNS Errors" registry Section 5.2. The 234 INFO-CODE from the EDE EDNS option is used to serve as an index into 235 the "Extended DNS Error" IANA registry, the initial values for which 236 are defined in the following sub-sections. 238 4.1. Extended DNS Error Code 0 - Other 240 The error in question falls into a category that does not match known 241 extended error codes. Implementations SHOULD include an EXTRA-TEXT 242 value to augment this error code with additional information. 244 4.2. Extended DNS Error Code 1 - Unsupported DNSKEY Algorithm 246 The resolver attempted to perform DNSSEC validation, but a DNSKEY 247 RRSET contained only unsupported DNSSEC algorithms. 249 4.3. Extended DNS Error Code 2 - Unsupported DS Digest Type 251 The resolver attempted to perform DNSSEC validation, but a DS RRSET 252 contained only unsupported Digest Types. 254 4.4. Extended DNS Error Code 3 - Stale Answer 256 The resolver was unable to resolve the answer within its time limits 257 and decided to answer with previously cached data instead of 258 answering with an error. This is typically caused by problems 259 communicating with an authoritative server, possibly as result of a 260 denial of service (DoS) attack against another network. (See also 261 Code 19.) 263 4.5. Extended DNS Error Code 4 - Forged Answer 265 For policy reasons (legal obligation, or malware filtering, for 266 instance), an answer was forged. Note that this should be used when 267 an answer is still provided, not when failure codes are returned 268 instead. See Blocked(15), Censored (16), and Filtered (17) for use 269 when returning other response codes. 271 4.6. Extended DNS Error Code 5 - DNSSEC Indeterminate 273 The resolver attempted to perform DNSSEC validation, but validation 274 ended in the Indeterminate state [RFC4035]. 276 4.7. Extended DNS Error Code 6 - DNSSEC Bogus 278 The resolver attempted to perform DNSSEC validation, but validation 279 ended in the Bogus state. 281 4.8. Extended DNS Error Code 7 - Signature Expired 283 The resolver attempted to perform DNSSEC validation, but no 284 signatures are presently valid and some (often all) are expired. 286 4.9. Extended DNS Error Code 8 - Signature Not Yet Valid 288 The resolver attempted to perform DNSSEC validation, but but no 289 signatures are presently valid and at least some are not yet valid. 291 4.10. Extended DNS Error Code 9 - DNSKEY Missing 293 A DS record existed at a parent, but no supported matching DNSKEY 294 record could be found for the child. 296 4.11. Extended DNS Error Code 10 - RRSIGs Missing 298 The resolver attempted to perform DNSSEC validation, but no RRSIGs 299 could be found for at least one RRset where RRSIGs were expected. 301 4.12. Extended DNS Error Code 11 - No Zone Key Bit Set 303 The resolver attempted to perform DNSSEC validation, but no Zone Key 304 Bit was set in a DNSKEY. 306 4.13. Extended DNS Error Code 12 - NSEC Missing 308 The resolver attempted to perform DNSSEC validation, but the 309 requested data was missing and a covering NSEC or NSEC3 was not 310 provided. 312 4.14. Extended DNS Error Code 13 - Cached Error 314 The resolver is returning the SERVFAIL RCODE from its cache. 316 4.15. Extended DNS Error Code 14 - Not Ready 318 The server is unable to answer the query as it was not fully 319 functional when the query was received. 321 4.16. Extended DNS Error Code 15 - Blocked 323 The server is unable to respond to the request because the domain is 324 blacklisted due to an internal security policy imposed by the 325 operator of the server resolving or forwarding the query. 327 4.17. Extended DNS Error Code 16 - Censored 329 The server is unable to respond to the request because the domain is 330 blacklisted due to an external requirement imposed by an entity other 331 than the operator of the server resolving or forwarding the query. 332 Note that how the imposed policy is applied is irrelevant (in-band 333 DNS filtering, court order, etc). 335 4.18. Extended DNS Error Code 17 - Filtered 337 The server is unable to respond to the request because the domain is 338 blacklisted as requested by the client. Functionally, this amounts 339 to "you requested that we filter domains like this one." 341 4.19. Extended DNS Error Code 18 - Prohibited 343 An authoritative server or recursive resolver that receives a query 344 from an "unauthorized" client can annotate its REFUSED message with 345 this code. Examples of "unauthorized" clients are recursive queries 346 from IP addresses outside the network, blacklisted IP addresses, 347 local policy, etc. 349 4.20. Extended DNS Error Code 19 - Stale NXDOMAIN Answer 351 The resolver was unable to resolve an answer within its configured 352 time limits and decided to answer with a previously cached NXDOMAIN 353 answer instead of answering with an error. This may be caused, for 354 example, by problems communicating with an authoritative server, 355 possibly as result of a denial of service (DoS) attack against 356 another network. (See also Code 3.) 358 4.21. Extended DNS Error Code 20 - Not Authoritative 360 An authoritative server that receives a query with the RD bit clear, 361 or when it is not configured for recursion for a domain for which it 362 is not authoritative SHOULD include this EDE code in the REFUSED 363 response. A resolver that receives a query with the RD bit clear 364 SHOULD include this EDE code in the REFUSED response. 366 4.22. Extended DNS Error Code 21 - Not Supported 368 The requested operation or query is not supported. 370 4.23. Extended DNS Error Code 22 - No Reachable Authority 372 The resolver could not reach any of the authoritative name servers 373 (or they potentially refused to reply). 375 4.24. Extended DNS Error Code 23 - Network Error 377 An unrecoverable error occurred while communicating with another 378 server. 380 4.25. Extended DNS Error Code 24 - Invalid Data 382 The authoritative server cannot answer with data for a zone it is 383 otherwise configured to support. Examples of this include its most 384 recent zone being too old, or having expired. 386 5. IANA Considerations 388 5.1. A New Extended DNS Error Code EDNS Option 390 This document defines a new EDNS(0) option, entitled "Extended DNS 391 Error", assigned a value of TBD from the "DNS EDNS0 Option Codes 392 (OPT)" registry [to be removed upon publication: 393 [http://www.iana.org/assignments/dns-parameters/dns- 394 parameters.xhtml#dns-parameters-11] 396 Value Name Status Reference 397 ----- ---------------- ------ ------------------ 398 TBD Extended DNS Error Standard [ This document ] 400 5.2. New Registry for Extended DNS Error Codes 402 IANA is requested to create and maintain a new registry table called 403 "Extended DNS Error Codes" on the "Domain Name System (DNS) 404 Parameters" web page as follows: 406 Registry Name: Extended DNS Error Codes 408 Registration Procedures: 410 o 0 - 49151: First come, first served. 411 o 49152 - 65535: Private use. 413 Reference: [this document] 415 The Extended DNS Error Codes registry is a table with three columns: 416 INFO-CODE, Purpose, and Reference. The initial contents is as below 417 with [this document] added to each reference given. 419 INFO-CODE: 0 420 Purpose: Other Error 421 Reference: Section 4.1 423 INFO-CODE: 1 424 Purpose: Unsupported DNSKEY Algorithm 425 Reference: Section 4.2 427 INFO-CODE: 2 428 Purpose: Unsupported DS Digest Type 429 Reference: Section 4.3 431 INFO-CODE: 3 432 Purpose: Stale Answer 433 Reference: Section 4.4, [RFC8767] 435 INFO-CODE: 4 436 Purpose: Forged Answer 437 Reference: Section 4.5 439 INFO-CODE: 5 440 Purpose: DNSSEC Indeterminate 441 Reference: Section 4.6 443 INFO-CODE: 6 444 Purpose: DNSSEC Bogus 445 Reference: Section 4.7 447 INFO-CODE: 7 448 Purpose: Signature Expired 449 Reference: Section 4.8 451 INFO-CODE: 8 452 Purpose: Signature Not Yet Valid 453 Reference: Section 4.9 455 INFO-CODE: 9 456 Purpose: DNSKEY Missing 457 Reference: Section 4.10 459 INFO-CODE: 10 460 Purpose: RRSIGs Missing 461 Reference: Section 4.11 463 INFO-CODE: 11 464 Purpose: No Zone Key Bit Set 465 Reference: Section 4.12 467 INFO-CODE: 12 468 Purpose: NSEC Missing 469 Reference: Section 4.13 471 INFO-CODE: 13 472 Purpose: Cached Error 473 Reference: Section 4.14 475 INFO-CODE: 14 476 Purpose: Not Ready. 477 Reference: Section 4.15 479 INFO-CODE: 15 480 Purpose: Blocked 481 Reference: Section 4.16 483 INFO-CODE: 16 484 Purpose: Censored 485 Reference: Section 4.17 487 INFO-CODE: 17 488 Purpose: Filtered 489 Reference: Section 4.18 491 INFO-CODE: 18 492 Purpose: Prohibited 493 Reference: Section 4.19 495 INFO-CODE: 19 496 Purpose: Stale NXDomain Answer 497 Reference: Section 4.20 499 INFO-CODE: 20 500 Purpose: Not Authoritative 501 Reference: Section 4.21 503 INFO-CODE: 21 504 Purpose: Not Supported 505 Reference: Section 4.22 507 INFO-CODE: 22 508 Purpose: No Reachable Authority 509 Reference: Section 4.23 511 INFO-CODE: 23 512 Purpose: Network Error 513 Reference: Section 4.24 515 INFO-CODE: 24 516 Purpose: Invalid Data 517 Reference: Section 4.25 519 INFO-CODE: 25-65535 520 Purpose: Unassigned 521 Reference: Section 5.2 523 6. Security Considerations 525 Though DNSSEC continues to be deployed, unfortunately a significant 526 number of clients (~11% according to [GeoffValidation]) that receive 527 a SERVFAIL from a validating resolver because of a DNSSEC validation 528 issue will simply ask the next (potentially non-validating) resolver 529 in their list, and thus don't get the protections which DNSSEC should 530 provide. 532 EDE information is unauthenticated information, unless secured by a 533 form of secured DNS transaction such as [RFC2845], [RFC2931], 534 [RFC8094] or [RFC8484]. An attacker (e.g a MITM or malicious 535 recursive server) could insert an extended error response into 536 untrusted data -- although ideally clients and resolvers would not 537 trust any unauthenticated information. As such, EDE content should 538 be treated only as diagnostic information and MUST NOT alter DNS 539 protocol processing. Until all DNS answers are authenticated via 540 DNSSEC or the other mechanisms mentioned above, there are some 541 tradeoffs. As an example, an attacker who is able to insert the 542 DNSSEC Bogus Extended Error into a DNS message could instead simply 543 reply with a fictitious address (A or AAAA) record. Note that DNS 544 Response Codes (RCODEs) also contain no authentication and can be 545 just as easily manipulated. 547 By design, EDE potentially exposes additional information DNS 548 resolution processes that may leak information. An example of this 549 is the Prohibited EDE code (18), which may leak the fact that the 550 name is on a blacklist. 552 7. Acknowledgements 554 The authors wish to thank Joe Abley, Mark Andrews, Tim April, 555 Vittorio Bertola, Stephane Bortzmeyer, Vladimir Cunat, Ralph Dolmans, 556 Peter DeVries, Peter van Dijk, Mats Dufberg, Donald Eastlake, Bob 557 Harold, Paul Hoffman, Geoff Huston, Shane Kerr, Edward Lewis, Carlos 558 M. Martinez, George Michelson, Eric Orth, Michael Sheldon, Puneet 559 Sood, Petr Spacek, Ondrej Sury, John Todd, Loganaden Velvindron, and 560 Paul Vixie. They also vaguely remember discussing this with a number 561 of people over the years, but have forgotten who all they were -- if 562 you were one of them, and are not listed, please let us know and 563 we'll acknowledge you. 565 One author also wants to thank the band "Infected Mushroom" for 566 providing a good background soundtrack (and to see if he can get away 567 with this in an RFC!). Another author would like to thank the band 568 "Mushroom Infectors". This was funny at the time we wrote it, but we 569 cannot remember why... 571 8. References 573 8.1. Normative References 575 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 576 Requirement Levels", BCP 14, RFC 2119, 577 DOI 10.17487/RFC2119, March 1997, 578 . 580 [RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S. 581 Rose, "Protocol Modifications for the DNS Security 582 Extensions", RFC 4035, DOI 10.17487/RFC4035, March 2005, 583 . 585 [RFC5198] Klensin, J. and M. Padlipsky, "Unicode Format for Network 586 Interchange", RFC 5198, DOI 10.17487/RFC5198, March 2008, 587 . 589 [RFC6891] Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms 590 for DNS (EDNS(0))", STD 75, RFC 6891, 591 DOI 10.17487/RFC6891, April 2013, 592 . 594 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 595 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 596 May 2017, . 598 [RFC8499] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS 599 Terminology", BCP 219, RFC 8499, DOI 10.17487/RFC8499, 600 January 2019, . 602 [RFC8767] Lawrence, D., Kumari, W., and P. Sood, "Serving Stale Data 603 to Improve DNS Resiliency", RFC 8767, 604 DOI 10.17487/RFC8767, March 2020, 605 . 607 8.2. Informative References 609 [GeoffValidation] 610 APNIC, G. H., "A quick review of DNSSEC Validation in 611 today's Internet", June 2016, . 614 [RFC2845] Vixie, P., Gudmundsson, O., Eastlake 3rd, D., and B. 615 Wellington, "Secret Key Transaction Authentication for DNS 616 (TSIG)", RFC 2845, DOI 10.17487/RFC2845, May 2000, 617 . 619 [RFC2931] Eastlake 3rd, D., "DNS Request and Transaction Signatures 620 ( SIG(0)s )", RFC 2931, DOI 10.17487/RFC2931, September 621 2000, . 623 [RFC8094] Reddy, T., Wing, D., and P. Patil, "DNS over Datagram 624 Transport Layer Security (DTLS)", RFC 8094, 625 DOI 10.17487/RFC8094, February 2017, 626 . 628 [RFC8484] Hoffman, P. and P. McManus, "DNS Queries over HTTPS 629 (DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018, 630 . 632 Authors' Addresses 634 Warren Kumari 635 Google 636 1600 Amphitheatre Parkway 637 Mountain View, CA 94043 638 US 640 Email: warren@kumari.net 642 Evan Hunt 643 ISC 644 950 Charter St 645 Redwood City, CA 94063 646 US 648 Email: each@isc.org 650 Roy Arends 651 ICANN 653 Email: roy.arends@icann.org 655 Wes Hardaker 656 USC/ISI 657 P.O. Box 382 658 Davis, CA 95617 659 US 661 Email: ietf@hardakers.net 662 David C Lawrence 663 Oracle + Dyn 664 150 Dow St 665 Manchester, NH 03101 666 US 668 Email: tale@dd.org